The family Boraginaceae consists of about 150 genera and 1500 species of beautiful and sun-loving herbs which often have an aura of dryness. Stems, leaves, and sepals are often covered with minute rigid hairs. The leaves are simple, spiral, and exstipulate. The inflorescences are cymes. The flowers are actinomorphic. The calyx is tubular and 5-lobed. The corolla is tubular, membranous, 5-lobed, and often with a unique type of blue. The androecium consists of five stamens. The gynoecium includes two carpels fused in a 2 or 4 locular ovary, each locule sheltering 1–2 ovules. The fruits are berries or nutlets. Plants in this family are known to produce poisonous pyrrolizidine alkaloids.
10.1.1.1 Alkanna tinctoria Tausch.
Synonyms: Anchusa tinctoria (L.) L.; Lithospermum tinctorium Ruiz & Pav.; Plagiobothrys myosotoides (Lehm.) Brand
Common names: Dyer’s alkanet, Spanish buglot; dineshavali (India); ratanjot (India; Pakistan); abukhalsa shankar (Iran); anik, havaciva otu (Turkey)
Habitat: Deserts, meadows, seashores
Distribution: Turkey, Iran
Botanical observation: This creeping to diffuse herb grows up to about 60 cm long. The stems are terete and hairy. The leaves are simple, decussate, sessile, and exstipulate. The blade is triangular, hairy, and about 1 cm long. The cymes are terminal and bout 3 cm long. The calyx is hairy and develops five lanceolate lobes. The corolla is membranous, tubular, up to about 8 mm long, blue, darker or yellowish at throat, and develops 5 oblong round lobes. The androecium includes 5 stamens, The ovary is 4-lobed and develops a slender style and a forked stigma. The nutlets are minute.
Medicinal uses: Burn (Turkey); smallpox (Cambodia, Laos, Vietnam); wounds (India; Iran; Turkey)
Broad-spectrum antibacterial halo developed by naphthoquinones: Alkannin and alkannin acetate inhibited the growth of Staphylococcus aureus (ATCC 25923), Staphylococcus epidermidis (ATCC 12228), Escherichia coli (ATCC 25922), Enterobacter cloacae (ATCC 13047), Klebsiella pneumoniae (ATCC 13883), and Pseudomonas aeruginosa (ATCC 227853) (Damianakos et al., 2012).
Strong antibacterial (Gram-positive) amphiphilic naphthoquinone: Alkannin (LogD 3.2 at pH 7.4; molecular mass = 288.2 g/mol) inhibited the growth of Staphylococcus aureus, methicillin-resistant Staphylococcus aureus, Enterococcus faecalis, vancomycin-resistant Enterococcus (F935, VanA), and vancomycin-resistant Enterococcus (CKU-18, VanB) with the MIC/MBC values of 6.2/12.5, 6.2/12.5, 50/50, 50/50, and 25/50 μg/mL, respectively (Shen et al., 2002).
Anticandidal halo developed by naphthoquinones: Alkannin and alkannin acetate inhibited the growth of Candida albicans (ATCC 10231), Candida tropicalis (ATCC 13801), and Candida glabrata (ATCC 28838) (Damianakos et al., 2012).
Commentaries
- The roots produce a series of naphthoquinones including alkannins, alkannin isovalerate, alkannin acetate, and alkannin angelate (Papageorgiou & Digenis, 1980).
- The exact antibacterial mode of action of alkannin and alkannin acetate is yet apparently unknown, but Plyta et al. (1998) observed the inhibition of topoisomerase I by alkannin and alkannin acetate via at least in part, complexation with Zn2+ since these naphthoquinones have adjacent ketone and hydroxy groups. One could observe the planar structure of naphthoquinones that favors DNA intercalation. Bacterial topoisomerase I is a zinc metalloprotein (Tse-Dinh and Beran-Steed, 1988). Consider that viral enzymes are not uncommonly zinc metalloproteins. RNA-dependent DNA polymerase from the avian myeloblastosis virus is a zinc-dependent enzyme and the severe acute respiratory syndrome-associated coronavirus and the severe acute respiratory syndrome-associated coronavirus 2 bind to the zinc metalloenzyme angiotensin-converting enzyme to penetrate the host cell (Doboszewska et al., 2020). Thus, natural products complexing or chelating zinc could be of value against COVID-19 and other coronaviruses.
- Alkannin and derivatives in this plant are most probably antiviral for (+)-RNA viruses (including coronaviruses), since shikonin (also known as (+)-alkannin) inhibited the replication of Japanese encephalitis virus in TE-671 cells with the IC50 value of 2.1 μg/mL and a selectivity index value of 835.2 (Lin et al., 2008).
- Unani practitioners in Iran consider the plant as hot and dry and as such it might have antiviral potentials
- In Turkey, Alkanna orientalis (L.) Boiss. (local name: Dikensiz kizilot) and Alkanna megacarpa A. DC (local name: Havaciva) are used to heal wounds.
References
- Damianakos, H., Kretschmer, N., Sykłowska-Baranek, K., Pietrosiuk, A., Bauer, R. and Chinou, I., 2012. Antimicrobial and cytotoxic isohexenylnaphthazarins from Arnebia euchroma (Royle) Jonst. (Boraginaceae) callus and cell suspension culture. Molecules, 17(12), pp. 14310–14322.
- Doboszewska, U., Wlaź, P., Nowak, G. and Młyniec, K., 2020. Targeting zinc metalloenzymes in coronavirus disease 2019. British Journal of Pharmacology, 177(21), pp. 4887–4898.
- Lin, C.W., Wu, C.F., Hsiao, N.W., Chang, C.Y., Li, S.W., Wan, L., Lin, Y.J. and Lin, W.Y., 2008. Aloe-emodin is an interferon-inducing agent with antiviral activity against Japanese encephalitis virus and enterovirus 71. International Journal of Antimicrobial Agents, 32(4), pp. 355–359.
- Papageorgiou, V.P. and Digenis, G.A., 1980. Isolation of two new alkannin esters from Alkanna tinctoria. Planta Medica, 39(05), pp. 81–84.
- Plyta, Z.F., Li, T., Papageorgiou, V.P., Mellidis, A.S., Assimopoulou, A.N., Pitsinos, E.N. and Couladouros, E.A., 1998. Inhibition of topoisomerase I by naphthoquinone derivatives. Bioorganic & Medicinal Chemistry Letters, 8(23), pp. 3385–3390.
- Shen, C.C., Syu, W.J., Li, S.Y., Lin, C.H., Lee, G.H. and Sun, C.M., 2002. Antimicrobial activities of naphthazarins from arnebia e uchroma. Journal of Natural Products, 65(12), pp. 1857–1862.
- Tse-Dinh, Y.C. and Beran-Steed, R.K., 1988. Escherichia coli DNA topoisomerase I is a zinc metalloprotein with three repetitive zinc-binding domains. Journal of Biological Chemistry, 263(31), pp. 15857–15859.
10.1.1.2 Anchusa hispida Forssk.
Synonym: Gastrocotyle hispida (Forssk.) Bunge
Common names: Fu qi cao (China); gul i gav zaban (Iran); khatol (Pakistan)
Habitat: Deserts
Distribution: Iran, Afghanistan, Pakistan, India
Botanical observation: This discrete and diffuse herb grows up to about 35 cm tall. The stems are terete and hairy. The leaves are simple, sessile, spiral, and exstipulate. The blade is narrowly spathulate or oblanceolate, hairy, and up to about 0.4−1 cm × 3–10 cm. The flowers are axillary and solitary. The calyx is tubular, 3 mm long, hairy, and develops 5 lanceolate and hairy lobes. The corolla is blue, about 4 mm long, and develops five ovate lobes around a throat marked with five tiny appendages. The androecium includes five stamens adnate to the corolla tube. The ovary is 4-lobed. The style is slender, minute, and forms a capitate stigma. The nutlets are about 4 mm across.
Medicinal use: Dysentery, urinary tract infection (Pakistan)
Commentaries
- The plant builds a series of poisonous pyrrolizidine alkaloids such as retrocenine, trachelanthamine, supinine, intermedine, and lycopsamine (El-Shazly et al., 2017). The antimicrobial mode of action of pyrrolizidine alkaloids has apparently not been studied, but they are known to be cytotoxic by inducing DNA alkylation (Wink, 2012).
- In Turkey, Anchusa azurea Miller (local name: Sigirdili), Anchusa leptophylla Roem. & Schult. (local name: Sigirdili), and Anchusa strigosa Banks & Sol. (local name: Guriz) are used to heal wounds, whereas Anchusa azurea Mill. (local name: Mljmjokasin) is used for pimples. Essential oil of flowers of Anchusa strigosa Banks & Sol. (100 μg/mL) inhibited the growth of Staphylococcus aureus, Staphylococcus epidermidis, Bacillus subtilis, Escherichia coli, and Klebsiella pneumoniae (Al-Salihi et al., 2009). Aqueous extract of An...
